As one of the derivatives in the context of MIMO techniques, SM is becoming a hot research area. Its basic idea is using both the transmit antenna index and the modulated symbol to convey messages, which improves the spectrum efficiency and reduces the cost of radio frequency chain [1]}. Compared to MIMO technique, SM plays a crucial role in balancing the transmit rate and the hardware cost. On the other hand, the broadcast nature of the wireless communication incurs that the desired receiver is vulnerable to hostile users, thus establishing a set of systematically secure transmission strategies becomes an imperative demand. In this section, we review the crucial transmission strategies of the physical layer security under the typical SM system and hybrid SM system respectively.
